Vibrating screens



Oct. 7, 1969 J. A. K.' TUOMAALA 7 ,0

- vram'rme scamaus Filed Oct. 24. 19s? U it d Sta e U.S. Cl. 209-346 2 Claims ABSTRACT OF THE DISCLOSURE.

An improvement in vibrating screens in which the vibrating movement is brought forth by means of rotating masses which together with their. drive motor are directly attached to a screening apparatus supported by resilient elements and in which the center of gravity of the whole vibrating system and the application point of the vibrating force are situated at the same side of the center line of the vibrating screen, so disposed that the vibrating force is applied to a point which is situated at the opposite side of the center of gravity of the whole system 1 with respect to the center line of the screen and that the spring constant of the springs supporting the screening apparatus and the vibrating frequency are so selected with respect to each other that the vibration is overcritical.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an improvement in vibrating screens e.g. for fibre stock, and particularly to the so called flat screens, in which the vibrating movement is brought forth by means of rotating eccentric masses and the vibrating portion is supported by resilient elements. In conventional vibrator-motor systems, a rotating shaft carries an unbalanced or eccentric weight, producing elliptical vibrations through centrifugal force as the weight rotates. It is well known that a pair of equal unbalanced weights in counter-rotation will automatically synchronize their motions to produce a resultant linear vibration. This occurs because the components of force attributable to each rotating weight cancel each other out except when the two weights are in conjunction, that is, when their angular positions coincide. The points of conjunction are obviously on a line passing through the center of rotation. Vibrating devices based on this principle are conventional components in a wide range of commercial uses.

Description of the prior art With screens of this type the usual practice has been to place the rotating unbalanced or eccentric masses on a shaft above the screen plate so that the shaft is fixedly mounted on the screen plate so as to vibrate synchronically with the same whereas the drive means of the shaft on which the eccentric mass is mounted is disposed on a base beside the screen. This construction has however the disadvantage that for power transmission from the drive motor to the shaft it is necessary to employ cardan axles, elastic couplings or belt drives, all of which have proved relatively short lived because of the severe operating conditions. To eliminate this disadvantage the eccentric masses bringing forth the vibration have been coupled together with their shaft directly to the motor to form a single unit and the unit thus formed has been fixed directly to the screen as a whole, the screen in turn being supported on resilient elements. The vibrating unit thus formed has always been placed adjacent the screens "ice center of gravity and above the same, or in case several units have been employed they have been placed symmetrically with respect to the center of gravity, always however as near as possible to the center of gravity. This arrangement has however the disadvantage that servicing and maintenance of the vibrating unit has become difficult since the screens can be of substantial dimensions and the vibrating unit has been situated substantially at the middle of the screen.

SUMMARY OF THE INVENTION The object of the improvement according to the present invention is to provide power transmission from the drive motor to the vibrating shaft on which the eccentric mass is mounted without utilizing cardan' axles, elastic couplings of belt drives; and to make the servicing and maintenance of the vibrating unit easier by the fact that according to this invention the vibrating unit can be situated-nearer the rim of the vibrating unit and thus is more accessible.

Brief description of the drawing The improvement according to the invention is more fully described in the following with reference to the accompanying schematic drawing, showing one embodiment of the screen utilizing the arrangement according to the invention as a sectional view.

In the drawing, reference numeral 1 indicates a drive motor, 2 refers to a vibrating device having the usual counter-rotatory eccentric masses conventionally arranged to'produce linear vibratory movement, firmly attached to a screen plate 3. The drive motor 1 is directly coupled to the vibrating device 2 whereby it will be situated near the outer wall of the screen plate 3, by virtue of which The spring forces are reprensented by q, the center of gravity by G, the vibratory force by F and the distance of the application point of the vibration force from the center of gravity by a, and the distance of the resultant of the spring forces Eq from the center of gravity by b.

DESCRIPTION 'OF THE PREFERRED EMBODIMENT The object of the invention is to fixedly mount the motor and vibrating assembly on the screen so that the center of gravity of the thus formed vibrating system and the application point of the vibrating force will be situated at the same side of the center line of the screen, and that the application point of the vibrating force will be situated outside the center of gravity. The spring fac- "tors of the springs supporting the whole system and the vibration frequency of the entire system are selected so with respect to each other, that the vibration will be overcritical, which means that the spring force q and the vibrating force F will be in the same phase or in other words act in the same direction. This is achieved with the equilibrium condition:

The invention is not restricted to the embodiment herein described and shown, but can be modified in various ways within the scope of the accompanying claims. Thus the screen arrangement can be suspended from springs.

I claim:

1. In a vibrating screen assembly of the type in which linear vibratory movement is effected by rotating eccentric masses, an arrangement for producing overcritical vibration comprising a screen supported for linear vibratory movement by springs secured to the screen, a vibrating mechanism including a motor and rotatable eccentric masses coupled to the motor for rotation by the motor, said vibrating mechanism being directly attached to the screen and supported by said springs to vibrate with the screen and to comprise therewith a vibratory system having its center of gravity remote from a center line of the screen, the vibrating mechanism being adapted to apply vibratory force at a point spaced from said center of gravity and on the opposite side of the center of gravity from said center line, and the eccentric masses being adapted to rotate at a speed higher than the natural vibration frequency of the vibratory system.

2. The assembly of claim 1 wherein the supporting 4 i t 7 springs are adapted to exert force in the same direction as the vibratory force.

References Cited UNITED STATES PATENTS 1,726,192 8 1929 Richardson 209-3 67 X 2,415,993 2/ 1947 Cottrell 2093 26 X 2,854,594 9/ 1958 Philippovic 3l0.54 3,014,587 12/ 1961 Philippovic 209326 FOREIGN PATENTS 299,902 11/ 1928 Great Britain.

TIM R. MILES, Primary Examiner U.S. Cl. X.R. 

